How do I evaluate a startup’s addressable market?

To generate a venture-sized return, a startup must be able to scale to enormous size. This translates to needing to address a very large market. Some VCs put this at at least $1B, others $2B, still others higher. When evaluating a market, what is relevant is not just the size of the market, but also what amount of that market the specific startup in question can capture based on its product/service and business model.